The present invention pertains generally to hydraulic tools and more particularly to a distributing valve which is capable of using seawater as a hydraulic fluid. In general, there are a limited number of motors which can be used for powering portable tools and other submersible equipment in the ocean, each of which has its various advantages and disadvantages. Electric motors, while feasible in principle, have not proved reliable, especially since numerous controls with high sensitivity are necessary to prevent electric shock which necessarily increases the complexity of the device and its overall cost. The inherent danger of such electrical motors due to the electric shock hazard has, in this manner, limited their use in a salt water environment.
Although air tools have been found to be useful and safe in a seawater environment, they also present several disadvantages and limitations. Although only a single connection is required to the water's surface, thereby providing good maneuverability, air tools introduce an excessive amount of bubbles at the point of operation which restricts vision and, in general, interferes with underwater work. In addition, air operated tools are basically inefficient especially at deeper water levels where the air must be compressed to the local pressure. Additionally, air is almost totally lacking in lubricating qualities which is quite important in preventing excessive wear.
Since the ocean itself is a hydraulic environment, it is logical to consider the use of hydraulic tools for underwater use. In a closed hydraulic system utilizing suitable hydraulic fluid, very high pressure outputs can safely be obtained with remarkably small motors. These motors are also capable of being quite efficient. With a petroleum-based hydraulic fluid of suitable viscosity, pressure losses are moderate with short lines, lubrication is excellent within the system, and the torque speed characteristics are almost constant over a wide range of operating characteristics.
While safe, practical and efficient, oil-filled closed hydraulic systems also have various limitations and disadvantages. Since conventional hydraulic fluids are normally lighter than water, hydraulic pressure drops below local ambient sea pressure prevent operation of the hydraulic tools without the application of greater pressures on the hydraulic fluid. The high pressure hydraulic hoses required to provide the extremely high hydraulic pressures needed at lower depths tend to be stiff and, in general, very hard to handle by a diver. The requirement of a second return hose imposes increased handling forces on a diver which, in many cases, render the hydraulic system unmanageable.
An open system using seawater as the hydraulic medium, on the other hand, eliminates many of these problems encountered with the hydraulic oil type system. In such an open system using seawater, only a single hose is required between the powered equipment and the tools, thereby immediately eliminating half of the handling forces imposed by the stiff hydraulic hoses. In addition, a seawater system has an obvious advantage in that leakage in either direction, i.e., either from or into the system, does not cause contamination. Furthermore, because seawater has a lower viscosity, lines carrying water can be considerably smaller to achieve a given pressure than the lines required in an oil-filled closed system.
The very properties of water which make it ideal as a hydraulic fluid in a seawater environment, however, have introduced various other problems related to efficiency, friction and wear. Specifically, the relatively high viscosity, good lubricating and essentially non-corroding properties of hydraulic oil in conventional multi-piston hydraulic motors allows for the use of low tolerances and dissimilar metals between mating parts. However, use of an electrolyte such as seawater as the hydraulic fluid medium prevents the use of mating parts which form galvanic pairs due to possible corrosion. Additionally, clearances between mating parts must be greatly reduced due to the low viscosity of water as the hydraulic medium. Otherwise, excessive leakage produces a very inefficient system. These problems have been successfully overcome in a device for converting high pressure water into mechanical force. However, the problems of excessively close tolerances, non-corroding pairs of metals, and low viscosity hydraulic fluid have prevented the successful development of a commutating or distributing valve which is a necessary component in any multi-piston hydraulic motor.